Heater may take various shapes depending on the shape of an object to be heated by the heater. A tubular shaped heater is disclosed in, for example, Japanese Patent Application Laid-Open Publication (JP-A) No. 2006-349513, and a plate-like heater is disclosed in, for example, Japanese Patent Application Laid-Open Publication (JP-A) No. 2005-332628.
The tubular heater disclosed in JP 2006-349513A, owned by the present assignee, as shown in FIG. 7 hereof, includes a tubular body 201 forming a ceramic heater incorporated in a gas sensor 202. When energized via conducting wires 203, 203, the ceramic heater 201 generates heat to thereby prevent dew condensation from occurring in a detection chamber of the gas sensor 202. In FIG. 7, the conducting wires 203, 203 are shown as if they are disposed in opposed relation to each other. However, this is only for purposes of illustration. In reality, the conducting wires 203, 203 are disposed side by side or in lateral juxtaposition on one radial side of a central axis of the tubular ceramic heater 201.
The thus arranged ceramic heater 201 is not fully satisfactory in that the temperature in the vicinity of the two juxtaposed conducing wires 203, 203 is relatively low, while the temperature at a portion diametrically opposed to the two juxtaposed conducting wires 203, 203 is relatively high. Thus the prior ceramic heater 201 cannot generate heat with a uniform temperature distribution. Furthermore, the conducting wires 203, 203 are disposed side by side and, hence, they are likely to cause a short circuit during manufacture or assembly of the ceramic heater 201.
FIG. 8 hereof shows a thermosensor 221 disclosed in JP 2005-332628A. The thermosensor 221 includes a rectangular printed-circuit board 222 on which a resistance pattern 223 and a connection pattern 224 are formed by printing. Core wires 225 are connected to the connection pattern 224. The connection pattern 224 facilitates easy connection of the core wires 225 to the thermosensor 221. The resistance pattern 223 can be used as a resistance pattern of a heater in which instance the core wires 225 are connected directly to the resistance pattern 223.
When the heater having the resistance pattern 223 is energized via the core wires 225, the temperature of the resistance pattern 223 is relatively high at a central portion thereof and relatively low in the vicinity of the core wires 225. Thus, regional temperature variations of the conventional heater are relatively large.